Chapter 1 - Variation Under Domestication

Causes of Variability
Effects of Habit
Correlation of Growth
Inheritance
Character of Domestic Varieties
Difficulty of distinguishing between Varieties and Species
Origin of Domestic Varieties from one or more Species
Domestic pigeons, their Differences and Origin
Principle of Selection anciently followed, its Effects
Methodical and Unconscious Selection
Unknown Origin of our Domestic Productions
Circumstances favourable to Man's power of Selection

WHEN we look to the individuals of the same variety or sub-variety of our
older cultivated plants and animals, one of the first points which
strikes us, is, that they generally differ much more from each other,
than do the individuals of any one species or variety in a state of
nature. When we reflect on the vast diversity of the plants and
animals which have been cultivated, and which have varied during all
ages under the most different climates and treatment, I think we are
driven to conclude that this greater variability is simply due to our
domestic productions having been raised under conditions of life not
so uniform as, and somewhat different from, those to which the
parent-species have been exposed under nature. There is, also, I
think, some probability in the view propounded by Andrew Knight, that
this variability may be partly connected with excess of food. It seems
pretty clear that organic beings must be exposed during several
generations to the new conditions of life to cause any appreciable
amount of variation; and that when the organisation has once begun to
vary, it generally continues to vary for many generations.
No case is on record of a variable being ceasing to be variable under
cultivation. Our oldest cultivated plants, such as wheat, still often
yield new varieties: our oldest domesticated animals are still capable
of rapid improvement or modification.

It has been disputed at what period of time the causes of
variability, whatever they may be, generally act; whether
during the early or late period of development of the embryo, or at
the instant of conception. Geoffroy St Hilaire's experiments show that
unnatural treatment of the embryo causes monstrosities; and
monstrosities cannot be separated by any clear line of distinction
from mere variations. But I am strongly inclined to suspect that the
most frequent cause of variability may be attributed to the male and
female reproductive elements having been affected prior to the act of
conception. Several reasons make me believe in this; but the chief one
is the remarkable effect which confinement or cultivation has on the
functions of the reproductive system; this system appearing to be far
more susceptible than any other part of the organization, to the
action of any change in the conditions of life. Nothing is more easy
than to tame an animal, and few things more difficult than to get it
to breed freely under confinement, even in the many cases when the
male and female unite. How many animals there are which will not
breed, though living long under not very close confinement in their
native country! This is generally attributed to vitiated instincts;
but how many cultivated plants display the utmost vigour, and yet
rarely or never seed! In some few such cases it has been found out
that very trifling changes, such as a little more or less water at
some particular period of growth, will determine whether or not the
plant sets a seed. I cannot here enter on the copious details which I
have collected on this curious subject; but to show how singular the
laws are which determine the reproduction of animals under
confinement, I may just mention that carnivorous animals, even from
the tropics, breed in this country pretty freely under confinement,
with the exception of the plantigrades or bear family; whereas,
carnivorous birds, with the rarest exceptions, hardly ever lay fertile
eggs. Many exotic plants have pollen utterly worthless, in the same
exact condition as in the most sterile hybrids. When, on the one hand,
we see domesticated animals and plants, though often weak and sickly,
yet breeding quite freely under confinement; and when, on the other
hand, we see individuals, though taken young from a state of nature,
perfectly tamed, long-lived, and healthy (of which I could give
numerous instances), yet having their reproductive system
so seriously affected by unperceived causes as to fail in acting, we
need not be surprised at this system, when it does act under
confinement, acting not quite regularly, and producing offspring not
perfectly like their parents or variable.

Sterility has been said to be the bane of horticulture; but on this
view we owe variability to the same cause which produces sterility;
and variability is the source of all the choicest productions of the
garden. I may add, that as some organisms will breed most freely under
the most unnatural conditions (for instance, the rabbit and ferret
kept in hutches), showing that their reproductive system has not been
thus affected; so will some animals and plants withstand domestication
or cultivation, and vary very slightly perhaps hardly more
than in a state of nature.

A long list could easily be given of 'sporting plants;' by this
term gardeners mean a single bud or offset, which suddenly assumes a
new and sometimes very different character from that of the rest of
the plant. Such buds can be propagated by grafting, &c., and
sometimes by seed. These 'sports' are extremely rare under nature,
but far from rare under cultivation; and in this case we see that the
treatment of the parent has affected a bud or offset, and not the
ovules or pollen. But it is the opinion of most physiologists that
there is no essential difference between a bud and an ovule in their
earliest stages of formation; so that, in fact,'sports' support my
view, that variability may be largely attributed to the ovules or
pollen, or to both, having been affected by the treatment of the
parent prior to the act of conception. These cases anyhow show that
variation is not necessarily connected, as some authors have supposed,
with the act of generation.

Seedlings from the same fruit, and the young of the same litter,
sometimes differ considerably from each other, though both the young
and the parents, as Muller has remarked, have apparently been exposed
to exactly the same conditions of life; and this shows how unimportant
the direct effects of the conditions of life are in comparison with
the laws of reproduction, and of growth, and of inheritance; for had
the action of the conditions been direct, if any of the young had
varied, all would probably have varied in the same manner. To judge
how much, in the case of any variation, we should
attribute to the direct action of heat, moisture, light, food,
&c., is most difficult: my impression is, that with animals such
agencies have produced very little direct effect, though apparently
more in the case of plants. Under this point of view, Mr Buckman's
recent experiments on plants seem extremely valuable. When all or
nearly all the individuals exposed to certain conditions are affected
in the same way, the change at first appears to be directly due to
such conditions; but in some cases it can be shown that quite opposite
conditions produce similar changes of structure. Nevertheless some
slight amount of change may, I think, be attributed to the direct
action of the conditions of life as, in some cases, increased
size from amount of food, colour from particular kinds of food and
from light, and perhaps the thickness of fur from climate.

Habit also has a deciding influence, as in the period of flowering
with plants when transported from one climate to another. In animals
it has a more marked effect; for instance, I find in the domestic duck
that the bones of the wing weigh less and the bones of the leg more,
in proportion to the whole skeleton, than do the same bones in the
wild-duck; and I presume that this change may be safely attributed to
the domestic duck flying much less, and walking more, than its wild
parent. The great and inherited development of the udders in cows and
goats in countries where they are habitually milked, in comparison
with the state of these organs in other countries, is another instance
of the effect of use. Not a single domestic animal can be named which
has not in some country drooping ears; and the view suggested by some
authors, that the drooping is due to the disuse of the muscles of the
ear, from the animals not being much alarmed by danger, seems
probable.

There are many laws regulating variation, some few of which can be
dimly seen, and will be hereafter briefly mentioned. I will here only
allude to what may be called correlation of growth. Any change in the
embryo or larva will almost certainly entail changes in the mature
animal. In monstrosities, the correlations between quite distinct
parts are very curious; and many instances are given in Isidore
Geoffroy St Hilaire's great work on this subject. Breeders believe
that long limbs are almost always accompanied by an
elongated head. Some instances of correlation are quite whimsical;
thus cats with blue eyes are invariably deaf; colour and
constitutional peculiarities go together, of which many remarkable
cases could be given amongst animals and plants. From the facts
collected by Heusinger, it appears that white sheep and pigs are
differently affected from coloured individuals by certain vegetable
poisons. Hairless dogs have imperfect teeth; long-haired and
coarse-haired animals are apt to have, as is asserted, long or many
horns; pigeons with feathered feet have skin between their outer toes;
pigeons with short beaks have small feet, and those with long beaks
large feet. Hence, if man goes on selecting, and thus augmenting, any
peculiarity, he will almost certainly unconsciously modify other parts
of the structure, owing to the mysterious laws of the correlation of
growth.

The result of the various, quite unknown, or dimly seen laws of
variation is infinitely complex and diversified. It is well worth
while carefully to study the several treatises published on some of
our old cultivated plants, as on the hyacinth, potato, even the
dahlia, &c.; and it is really surprising to note the endless
points in structure and constitution in which the varieties and sub
varieties differ slightly from each other. The whole organization
seems to have become plastic, and tends to depart in some small degree
from that of the parental type.

Any variation which is not inherited is unimportant for us. But the
number and diversity of inheritable deviations of structure, both
those of slight and those of considerable physiological importance, is
endless. Dr Prosper Lucas's treatise, in two large volumes, is the
fullest and the best on this subject. No breeder doubts how strong is
the tendency to inheritance: like produces like is his fundamental
belief: doubts have been thrown on this principle by theoretical
writers alone. When a deviation appears not unfrequently, and we see
it in the father and child, we cannot tell whether it may not be due
to the same original cause acting on both; but when amongst
individuals, apparently exposed to the same conditions, any very rare
deviation, due to some extraordinary combination of circumstances,
appears in the parent say, once amongst several million
individuals and it reappears in the child, the
mere doctrine of chances almost compels us to attribute its
reappearance to inheritance. Every one must have heard of cases of
albinism, prickly skin, hairy bodies, &c. appearing in several
members of the same family. If strange and rare deviations of
structure are truly inherited, less strange and commoner deviations
may be freely admitted to be inheritable. Perhaps the correct way of
viewing the whole subject, would be, to look at the inheritance of
every character whatever as the rule, and non-inheritance as the
anomaly.

The laws governing inheritance are quite unknown; no one can say
why the same peculiarity in different individuals of the same species,
and in individuals of different species, is sometimes inherited and
sometimes not so; why the child often reverts in certain characters to
its grandfather or grandmother or other much more remote ancestor; why
a peculiarity is often transmitted from one sex to both sexes or to
one sex alone, more commonly but not exclusively to the like sex. It
is a fact of some little importance to us, that peculiarities
appearing in the males of our domestic breeds are often transmitted
either exclusively, or in a much greater degree, to males alone. A
much more important rule, which I think may be trusted, is that, at
whatever period of life a peculiarity first appears, it tends to
appear in the offspring at a corresponding age, though sometimes
earlier. In many cases this could not be otherwise: thus the inherited
peculiarities in the horns of cattle could appear only in the
offspring when nearly mature; peculiarities in the silkworm are known
to appear at the corresponding caterpillar or cocoon stage. But
hereditary diseases and some other facts make me believe that the rule
has a wider extension, and that when there is no apparent reason why a
peculiarity should appear at any particular age, yet that it does tend
to appear in the offspring at the same period at which it first
appeared in the parent. I believe this rule to be of the highest
importance in explaining the laws of embryology. These remarks are of
course confined to the first appearance of
the peculiarity, and not to its primary cause, which may have acted on
the ovules or male element; in nearly the same manner as in the
crossed offspring from a short-horned cow by a long-horned bull, the
greater length of horn, though appearing late in life, is
clearly due to the male element.

Having alluded to the subject of reversion, I may here refer to a
statement often made by naturalists namely, that our domestic
varieties, when run wild, gradually but certainly revert in character
to their aboriginal stocks. Hence it has been argued that no
deductions can be drawn from domestic races to species in a state of
nature. I have in vain endeavoured to discover on what decisive facts
the above statement has so often and so boldly been made. There would
be great difficulty in proving its truth: we may safely conclude that
very many of the most strongly-marked domestic varieties could not
possibly live in a wild state. In many cases we do not know what the
aboriginal stock was, and so could not tell whether or not nearly
perfect reversion had ensued. It would be quite necessary, in order to
prevent the effects of intercrossing, that only a single variety
should be turned loose in its new home. Nevertheless, as our
varieties certainly do occasionally revert in some of their characters
to ancestral forms, it seems to me not improbable, that if we could
succeed in naturalising, or were to cultivate, during many
generations, the several races, for instance, of the cabbage, in very
poor soil (in which case, however, some effect would have to be
attributed to the direct action of the poor soil), that they would to
a large extent, or even wholly, revert to the wild aboriginal stock.
Whether or not the experiment would succeed, is not of great
importance for our line of argument; for by the experiment itself the
conditions of life are changed. If it could be shown that our domestic
varieties manifested a strong tendency to reversion, that is,
to lose their acquired characters, whilst kept under unchanged
conditions, and whilst kept in a considerable body, so that free
intercrossing might check, by blending together, any slight deviations
of structure, in such case, I grant that we could deduce nothing from
domestic varieties in regard to species. But there is not a shadow of
evidence in favour of this view: to assert that we could not breed our
cart and race-horses, long and short-horned cattle and poultry of
various breeds, and esculent vegetables, for an almost infinite number
of generations, would be opposed to all experience. I may add, that
when under nature the conditions of life do change,
variations and reversions of character probably do occur; but natural
selection, as will hereafter be explained, will determine how far the
new characters thus arising shall be preserved.

When we look to the hereditary varieties or races of our domestic
animals and plants, and compare them with species closely allied
together, we generally perceive in each domestic race, as already
remarked, less uniformity of character than in true species. Domestic
races of the same species, also, often have a somewhat monstrous
character; by which I mean, that, although differing from each other,
and from the other species of the same genus, in several trifling
respects, they often differ in an extreme degree in some one part,
both when compared one with another, and more especially when compared
with all the species in nature to which they are nearest allied. With
these exceptions (and with that of the perfect fertility of varieties
when crossed, a subject hereafter to be discussed), domestic
races of the same species differ from each other in the same manner
as, only in most cases in a lesser degree than, do closely-allied
species of the same genus in a state of nature. I think this must be
admitted, when we find that there are hardly any domestic races,
either amongst animals or plants, which have not been ranked by some
competent judges as mere varieties, and by other competent judges as
the descendants of aboriginally distinct species. If any marked
distinction existed between domestic races and species, this source of
doubt could not so perpetually recur. It has often been stated that
domestic races do not differ from each other in characters of generic
value. I think it could be shown that this statement is hardly
correct; but naturalists differ most widely in determining what
characters are of generic value; all such valuations being at present
empirical. Moreover, on the view of the origin of genera which I shall
presently give, we have no right to expect often to meet with generic
differences in our domesticated productions.

When we attempt to estimate the amount of structural difference
between the domestic races of the same species, we are soon involved
in doubt, from not knowing whether they have descended
from one or several parent-species. This point, if could be cleared
up, would be interesting; if, for instance, it could be shown that the
greyhound, bloodhound, terrier, spaniel, and bull-dog, which we all
know propagate their kind so truly, were the offspring of any single
species, then such facts would have great weight in making us doubt
about the immutability of the many very closely allied and natural
species for instance, of the many foxes inhabiting
different quarters of the world. I do not believe, as we shall
presently see, that all our dogs have descended from any one wild
species; but, in the case of some other domestic races, there is
presumptive, or even strong, evidence in favour of this view.

It has often been assumed that man has chosen for domestication
animals and plants having an extraordinary inherent tendency to vary,
and likewise to withstand diverse climates. I do not dispute that
these capacities have added largely to the value of most of our
domesticated productions; but how could a savage possibly know, when
he first tamed an animal, whether it would vary in succeeding
generations, and whether it would endure other climates? Has the
little variability of the ass or guinea-fowl, or the small power of
endurance of warmth by the reindeer, or of cold by the common camel,
prevented their domestication? I cannot doubt that if other animals
and plants, equal in number to our domesticated productions, and
belonging to equally diverse classes and countries, were taken from a
state of nature, and could be made to breed for an equal number of
generations under domestication, they would vary on an average as
largely as the parent species of our existing domesticated productions
have varied.

In the case of most of our anciently domesticated animals and
plants, I do not think it is possible to come to any definite
conclusion, whether they have descended from one or several species.
The argument mainly relied on by those who believe in the multiple
origin of our domestic animals is, that we find in the most ancient
records, more especially on the monuments of Egypt, much diversity in
the breeds; and that some of the breeds closely resemble, perhaps are
identical with, those still existing. Even if this latter fact were
found more strictly and generally true than seems to me to
be the case, what does it show, but that some of our breeds originated
there, four or five thousand years ago? But Mr Horner's
researches have rendered it in some degree probable that man
sufficiently civilized to have manufactured pottery existed in the
valley of the Nile thirteen or fourteen thousand years ago; and who
will pretend to say how long before these ancient periods, savages,
like those of Tierra del Fuego or Australia, who possess a
semi-domestic dog, may not have existed in Egypt?

The whole subject must, I think, remain vague; nevertheless, I may,
without here entering on any details, state that, from geographical
and other considerations, I think it highly probable that our domestic
dogs have descended from several wild species. In regard to sheep and
goats I can form no opinion. I should think, from facts communicated
to me by Mr Blyth, on the habits, voice, and constitution, &c., of
the humped Indian cattle, that these had descended from a different
aboriginal stock from our European cattle; and several competent
judges believe that these latter have had more than one wild parent.
With respect to horses, from reasons which I cannot give here, I am
doubtfully inclined to believe, in opposition to several authors, that
all the races have descended from one wild stock. Mr Blyth, whose
opinion, from his large and varied stores of knowledge, I should value
more than that of almost any one, thinks that all the breeds of
poultry have proceeded from the common wild Indian fowl (Gallus
bankiva). In regard to ducks and rabbits, the breeds of which differ
considerably from each other in structure, I do not doubt that they
all have descended from the common wild duck and rabbit.

The doctrine of the origin of our several domestic races from
several aboriginal stocks, has been carried to an absurd extreme by
some authors. They believe that every race which breeds true, let the
distinctive characters be ever so slight, has had its wild prototype.
At this rate there must have existed at least a score of species of
wild cattle, as many sheep, and several goats in Europe alone, and
several even within Great Britain. One author believes that there
formerly existed in Great Britain eleven wild species of sheep
peculiar to it! When we bear in mind that Britain has
now hardly one peculiar mammal, and France but few distinct from those
of Germany and conversely, and so with Hungary, Spain, &c., but
that each of these kingdoms possesses several peculiar breeds of
cattle, sheep, &c., we must admit that many domestic breeds have
originated in Europe; for whence could they have been derived, as
these several countries do not possess a number of peculiar species as
distinct parent-stocks? So it is in India. Even in the case of the
domestic dogs of the whole world, which I fully admit have probably
descended from several wild species, I cannot doubt that there has
been an immense amount of inherited variation. Who can believe that
animals closely resembling the Italian greyhound, the bloodhound, the
bull-dog, or Blenheim spaniel, &c. so unlike all wild
Canidae ever existed freely in a state of nature? It has often
been loosely said that all our races of dogs have been produced by the
crossing of a few aboriginal species; but by crossing we can get only
forms in some degree intermediate between their parents; and if we
account for our several domestic races by this process, we must admit
the former existence of the most extreme forms, as the Italian
greyhound, bloodhound, bull-dog, &c., in the wild state. Moreover,
the possibility of making distinct races by crossing has been greatly
exaggerated. There can be no doubt that a race may be modified by
occasional crosses, if aided by the careful selection of those
individual mongrels, which present any desired character; but that a
race could be obtained nearly intermediate between two extremely
different races or species, I can hardly
believe. Sir J. Sebright expressly experimentised for this object, and
failed. The offspring from the first cross between two pure breeds is
tolerably and sometimes (as I have found with pigeons) extremely
uniform, and everything seems simple enough; but when these mongrels
are crossed one with another for several generations, hardly two of
them will be alike, and then the extreme difficulty, or rather utter
hopelessness, of the task becomes apparent. Certainly, a breed
intermediate between two very distinct breeds could not be got without extreme
care and long-continued selection; nor can I find a single case on
record of a permanent race having been thus formed.

On the Breeds of the Domestic pigeon.

Believing that it is always best to study some special
group, I have, after deliberation, taken up domestic pigeons. I have
kept every breed which I could purchase or obtain, and have been most
kindly favoured with skins from several quarters of the world, more
especially by the Hon. W. Elliot from India, and by the Hon. C.
Murray from Persia. Many treatises in different languages have been
published on pigeons, and some of them are very important, as being of
considerably antiquity. I have associated with several eminent
fanciers, and have been permitted to join two of the London Pigeon
Clubs. The diversity of the breeds is something astonishing. Compare
the English carrier and the short-faced tumbler, and see the wonderful
difference in their beaks, entailing corresponding differences in
their skulls. The carrier, more especially the male bird, is also
remarkable from the wonderful development of the carunculated skin
about the head, and this is accompanied by greatly elongated eyelids,
very large external orifices to the nostrils, and a wide gape of
mouth. The short-faced tumbler has a beak in outline almost like that
of a finch; and the common tumbler has the singular and strictly
inherited habit of flying at a great height in a compact flock, and
tumbling in the air head over heels. The runt is a bird of great size,
with long, massive beak and large feet; some of the sub-breeds of
runts have very long necks, others very long wings and tails, others
singularly short tails. The barb is allied to the carrier, but,
instead of a very long beak, has a very short and very broad one. The
pouter has a much elongated body, wings, and legs; and its enormously
developed crop, which it glories in inflating, may well excite
astonishment and even laughter. The turbit has a very short and
conical beak, with a line of reversed feathers down the breast; and it
has the habit of continually expanding slightly the upper part of the
oesophagus. The Jacobin has the feathers so much reversed along the
back of the neck that they form a hood, and it has, proportionally to
its size, much elongated wing and tail feathers. The trumpeter and
laugher, as their names express, utter a very different coo from the
other breeds. The fantail has thirty or even forty tail-feathers,
instead of twelve or fourteen, the normal number in all members of the
great pigeon family; and these feathers are kept expanded, and are
carried so erect that in good birds the head and tail
touch; the oil-gland is quite aborted. Several other less distinct
breeds might have been specified.

In the skeletons of the several breeds, the development of the
bones of the face in length and breadth and curvature differs
enormously. The shape, as well as the breadth and length of the ramus
of the lower jaw, varies in a highly remarkable manner. The number of
the caudal and sacral vertebrae vary; as does the number of the ribs,
together with their relative breadth and the presence of processes.
The size and shape of the apertures in the sternum are highly
variable; so is the degree of divergence and relative size of the two
arms of the furcula. The proportional width of the gape of mouth, the
proportional length of the eyelids, of the orifice of the nostrils, of
the tongue (not always in strict correlation with the length of beak),
the size of the crop and of the upper part of the oesophagus; the
development and abortion of the oil-gland; the number of the primary
wing and caudal feathers; the relative length of wing and tail to each
other and to the body; the relative length of leg and of the feet; the
number of scutellae on the toes, the development of skin between the
toes, are all points of structure which are variable. The period at
which the perfect plumage is acquired varies, as does the state of the
down with which the nestling birds are clothed when hatched. The shape
and size of the eggs vary. The manner of flight differs remarkably; as
does in some breeds the voice and disposition. Lastly, in certain
breeds, the males and females have come to differ to a slight degree
from each other.

Altogether at least a score of pigeons might be chosen, which if
shown to an ornithologist, and he were told that they were wild birds,
would certainly, I think, be ranked by him as well-defined species.
Moreover, I do not believe that any ornithologist would place
the English carrier, the short-faced tumbler, the runt, the barb, pouter,
and fantail in the same genus; more especially as in each of these
breeds several truly-inherited sub-breeds, or species as he might have
called them, could be shown him.

Great as the differences are between the breeds of pigeons, I am
fully convinced that the common opinion of naturalists is correct,
namely, that all have descended from the rock-pigeon
(Columba livia), including under this term several geographical races
or sub-species, which differ from each other in the most trifling
respects. As several of the reasons which have led me to this belief
are in some degree applicable in other cases, I will here briefly give
them. If the several breeds are not varieties, and have not proceeded
from the rock-pigeon, they must have descended from at least seven or
eight aboriginal stocks; for it is impossible to make the present
domestic breeds by the crossing of any lesser number: how, for
instance, could a pouter be produced by crossing two breeds unless one
of the parent-stocks possessed the characteristic enormous crop? The
supposed aboriginal stocks must all have been rock-pigeons, that is,
not breeding or willingly perching on trees. But besides C. livia,
with its geographical sub-species, only two or three other species of
rock-pigeons are known; and these have not any of the characters of
the domestic breeds. Hence the supposed aboriginal stocks must either
still exist in the countries where they were originally domesticated,
and yet be unknown to ornithologists; and this, considering their
size, habits, and remarkable characters, seems very improbable; or
they must have become extinct in the wild state. But birds breeding on
precipices, and good fliers, are unlikely to be exterminated; and the
common rock-pigeon, which has the same habits with the domestic
breeds, has not been exterminated even on several of the smaller
British islets, or on the shores of the Mediterranean. Hence the
supposed extermination of so many species having similar habits with
the rock-pigeon seems to me a very rash assumption. Moreover, the
several above-named domesticated breeds have been transported to all
parts of the world, and, therefore, some of them must have been
carried back again into their native country; but not one has ever
become wild or feral, though the dovecot-pigeon, which is the
rock-pigeon in a very slightly altered state, has become feral in
several places. Again, all recent experience shows that it is most
difficult to get any wild animal to breed freely under domestication;
yet on the hypothesis of the multiple origin of our pigeons, it must
be assumed that at least seven or eight species were so thoroughly
domesticated in ancient times by half-civilized man, as to be quite
prolific under confinement.

An argument, as it seems to me, of great weight, and applicable in
several other cases, is, that the above-specified breeds, though
agreeing generally in constitution, habits, voice, colouring, and in
most parts of their structure, with the wild rock-pigeon, yet are
certainly highly abnormal in other parts of their structure: we may
look in vain throughout the whole great family of Columbidae for a
beak like that of the English carrier, or that of the short-faced
tumbler, or barb; for reversed feathers like those of the jacobin; for
a crop like that of the pouter; for tail-feathers like those of the
fantail. Hence it must be assumed not only that half-civilized man
succeeded in thoroughly domesticating several species, but that he
intentionally or by chance picked out extraordinarily abnormal
species; and further, that these very species have since all become
extinct or unknown. So many strange contingencies seem to me
improbable in the highest degree.

Some facts in regard to the colouring of pigeons well deserve
consideration. The rock-pigeon is of a slaty-blue, and has a white
rump (the Indian sub-species, C. intermedia of Strickland, having it
bluish); the tail has a terminal dark bar, with the bases of the outer
feathers externally edged with white; the wings have two black bars:
some semi-domestic breeds and some apparently truly wild breeds have,
besides the two black bars, the wings chequered with black. These
several marks do not occur together in any other species of the whole
family. Now, in every one of the domestic breeds, taking thoroughly
well-bred birds, all the above marks, even to the white edging of the
outer tail-feathers, sometimes concur perfectly developed. Moreover,
when two birds belonging to two distinct breeds are crossed, neither
of which is blue or has any of the above-specified marks, the mongrel
offspring are very apt suddenly to acquire these characters; for
instance, I crossed some uniformly white fantails with some uniformly
black barbs, and they produced mottled brown and black birds; these I
again crossed together, and one grandchild of the pure white fantail
and pure black barb was of as beautiful a blue colour, with the white
rump, double black wing-bar, and barred and white-edged tail-feathers,
as any wild rock-pigeon! We can understand these facts, on the
well-known principle of reversion to ancestral characters,
if all the domestic breeds have descended from the rock-pigeon. But if
we deny this, we must make one of the two following highly improbable
suppositions. Either, firstly, that all the several imagined
aboriginal stocks were coloured and marked like the rock-pigeon,
although no other existing species is thus coloured and marked, so
that in each separate breed there might be a tendency to revert to the
very same colours and markings. Or, secondly, that each breed, even
the purest, has within a dozen or, at most, within a score of
generations, been crossed by the rock-pigeon: I say within a dozen or
twenty generations, for we know of no fact countenancing the belief
that the child ever reverts to some one ancestor, removed by a greater
number of generations. In a breed which has been crossed only once
with some distinct breed, the tendency to reversion to any character
derived from such cross will naturally become less and less, as in
each succeeding generation there will be less of the foreign blood;
but when there has been no cross with a distinct breed, and there is a
tendency in both parents to revert to a character, which has been lost
during some former generation, this tendency, for all that we can see
to the contrary, may be transmitted undiminished for an indefinite
number of generations. These two distinct cases are often confounded
in treatises on inheritance.

Lastly, the hybrids or mongrels from between all the domestic
breeds of pigeons are perfectly fertile. I can state this from my own
observations, purposely made on the most distinct breeds. Now, it is
difficult, perhaps impossible, to bring forward one case of the hybrid
offspring of two animals clearly distinct
being themselves perfectly fertile. Some authors believe that
long-continued domestication eliminates this strong tendency to
sterility: from the history of the dog I think there is some
probability in this hypothesis, if applied to species closely related
together, though it is unsupported by a single experiment. But to
extend the hypothesis so far as to suppose that species, aboriginally
as distinct as carriers, tumblers, pouters, and fantails now are,
should yield offspring perfectly fertile, inter
se, seems to me rash in the extreme.

From these several reasons, namely, the improbability of man
having formerly got seven or eight supposed species of pigeons
to breed freely under domestication; these supposed species being
quite unknown in a wild state, and their becoming nowhere feral; these
species having very abnormal characters in certain respects, as
compared with all other Columbidae, though so like in most other
respects to the rock-pigeon; the blue colour and various marks
occasionally appearing in all the breeds, both when kept pure and when
crossed; the mongrel offspring being perfectly fertile; from
these several reasons, taken together, I can feel no doubt that all
our domestic breeds have descended from the Columba livia with its
geographical sub-species.

In favour of this view, I may add, firstly, that C. livia, or the
rock-pigeon, has been found capable of domestication in Europe and in
India; and that it agrees in habits and in a great number of points of
structure with all the domestic breeds. Secondly, although an English
carrier or short-faced tumbler differs immensely in certain characters
from the rock-pigeon, yet by comparing the several sub-breeds of these
breeds, more especially those brought from distant countries, we can
make an almost perfect series between the extremes of structure.
Thirdly, those characters which are mainly distinctive of each breed,
for instance the wattle and length of beak of the carrier, the
shortness of that of the tumbler, and the number of tail-feathers in
the fantail, are in each breed eminently variable; and the explanation
of this fact will be obvious when we come to treat of selection.
Fourthly, pigeons have been watched, and tended with the utmost care,
and loved by many people. They have been domesticated for thousands of
years in several quarters of the world; the earliest known record of
pigeons is in the fifth Aegyptian dynasty, about 3000 B.C., as was
pointed out to me by Professor Lepsius; but Mr Birch informs me that
pigeons are given in a bill of fare in the previous dynasty. In the
time of the Romans, as we hear from Pliny, immense prices were given
for pigeons; 'nay, they are come to this pass, that they can reckon up
their pedigree and race.' Pigeons were much valued by Akber Khan in
India, about the year 1600; never less than 20,000 pigeons were taken
with the court. 'The monarchs of Iran and Turan sent him some very
rare birds;' and, continues the courtly historian, 'His
Majesty by crossing the breeds, which method was never practised
before, has improved them astonishingly.' About this same period the
Dutch were as eager about pigeons as were the old Romans. The
paramount importance of these considerations in explaining the immense
amount of variation which pigeons have undergone, will be obvious when
we treat of Selection. We shall then, also, see how it is that the
breeds so often have a somewhat monstrous character. It is also a most
favourable circumstance for the production of distinct breeds, that
male and female pigeons can be easily mated for life; and thus
different breeds can be kept together in the same aviary.

I have discussed the probable origin of domestic pigeons at some,
yet quite insufficient, length; because when I first kept pigeons and
watched the several kinds, knowing well how true they bred, I felt
fully as much difficulty in believing that they could ever have
descended from a common parent, as any naturalist could in coming to a
similar conclusion in regard to the many species of finches, or other
large groups of birds, in nature. One circumstance has struck me much;
namely, that all the breeders of the various domestic animals and the
cultivators of plants, with whom I have ever conversed, or whose
treatises I have read, are firmly convinced that the several breeds to
which each has attended, are descended from so many aboriginally
distinct species. Ask, as I have asked, a celebrated raiser of
Hereford cattle, whether his cattle might not have descended from long
horns, and he will laugh you to scorn. I have never met a pigeon, or
poultry, or duck, or rabbit fancier, who was not fully convinced that
each main breed was descended from a distinct species. Van Mons, in
his treatise on pears and apples, shows how utterly he disbelieves
that the several sorts, for instance a Ribston-pippin or Codlin-apple,
could ever have proceeded from the seeds of the same tree. Innumerable
other examples could be given. The explanation, I think, is simple:
from long-continued study they are strongly impressed with the
differences between the several races; and though they well know that
each race varies slightly, for they win their prizes by selecting such
slight differences, yet they ignore all general arguments, and refuse
to sum up in their minds slight differences accumulated during
many successive generations. May not those naturalists who,
knowing far less of the laws of inheritance than does the breeder, and
knowing no more than he does of the intermediate links in the long
lines of descent, yet admit that many of our domestic races have
descended from the same parents may they not learn a lesson of
caution, when they deride the idea of species in a state of nature
being lineal descendants of other species?

Selection

Let us now briefly consider
the steps by which domestic races have been produced, either from one
or from several allied species. Some little effect may, perhaps, be
attributed to the direct action of the external conditions of life,
and some little to habit; but he would be a bold man who would account
by such agencies for the differences of a dray and race horse, a
greyhound and bloodhound, a carrier and tumbler pigeon. One of the
most remarkable features in our domesticated races is that we see in
them adaptation, not indeed to the animal's or plant's own good, but
to man's use or fancy. Some variations useful to him have probably
arisen suddenly, or by one step; many botanists, for instance, believe
that the fuller's teazle, with its hooks, which cannot be rivalled by
any mechanical contrivance, is only a variety of the wild Dipsacus;
and this amount of change may have suddenly arisen in a seedling. So
it has probably been with the turnspit dog; and this is known to have
been the case with the ancon sheep. But when we compare the
dray-horse and race-horse, the dromedary and camel, the various breeds
of sheep fitted either for cultivated land or mountain pasture, with
the wool of one breed good for one purpose, and that of another breed
for another purpose; when we compare the many breeds of dogs, each
good for man in very different ways; when we compare the gamecock, so
pertinacious in battle, with other breeds so little quarrelsome, with
'everlasting layers' which never desire to sit, and with the bantam so
small and elegant; when we compare the host of agricultural, culinary,
orchard, and flower-garden races of plants, most useful to man at
different seasons and for different purposes, or so beautiful in his
eyes, we must, I think, look further than to mere variability. We
cannot suppose that all the breeds were suddenly produced as perfect
and as useful as we now see them; indeed, in several
cases, we know that this has not been their history. The key is man's
power of accumulative selection: nature gives successive variations;
man adds them up in certain directions useful to him. In this sense he
may be said to make for himself useful breeds.

The great power of this principle of selection is not hypothetical.
It is certain that several of our eminent breeders have, even within a
single lifetime, modified to a large extent some breeds of cattle and
sheep. In order fully to realise what they have done, it is almost
necessary to read several of the many treatises devoted to this
subject, and to inspect the animals. Breeders habitually speak of an
animal's organisation as something quite plastic, which they can model
almost as they please. If I had space I could quote numerous passages
to this effect from highly competent authorities. Youatt, who was
probably better acquainted with the works of agriculturalists than
almost any other individual, and who was himself a very good judge of
an animal, speaks of the principle of selection as 'that which enables
the agriculturist, not only to modify the character of his flock, but
to change it altogether. It is the magician's wand, by means of which
he may summon into life whatever form and mould he pleases.' Lord
Somerville, speaking of what breeders have done for sheep, says:
'It would seem as if they had chalked out upon a wall a form
perfect in itself, and then had given it existence.' That most skilful
breeder, Sir John Sebright, used to say, with respect to pigeons, that
'he would produce any given feather in three years, but it would take
him six years to obtain head and beak.' In Saxony the importance of
the principle of selection in regard to merino sheep is so fully
recognised, that men follow it as a trade: the sheep are placed on a
table and are studied, like a picture by a connoisseur; this is done
three times at intervals of months, and the sheep are each time marked
and classed, so that the very best may ultimately be selected for
breeding.

What English breeders have actually effected is proved by the
enormous prices given for animals with a good pedigree; and these have
now been exported to almost every quarter of the world. The
improvement is by no means generally due to crossing different breeds;
all the best breeders are strongly opposed to this practice, except
sometimes amongst closely allied sub-breeds. And when a
cross has been made, the closest selection is far more indispensable
even than in ordinary cases. If selection consisted merely in
separating some very distinct variety, and breeding from it, the
principle would be so obvious as hardly to be worth notice; but its
importance consists in the great effect produced by the accumulation
in one direction, during successive generations, of differences
absolutely inappreciable by an uneducated eye differences
which I for one have vainly attempted to appreciate. Not one man in a
thousand has accuracy of eye and judgement sufficient to become an
eminent breeder. If gifted with these qualities, and he studies his
subject for years, and devotes his lifetime to it with indomitable
perseverance, he will succeed, and may make great improvements; if he
wants any of these qualities, he will assuredly fail. Few would
readily believe in the natural capacity and years of practice
requisite to become even a skilful pigeon-fancier.

The same principles are followed by horticulturists; but the
variations are here often more abrupt. No one supposes that our
choicest productions have been produced by a single variation from the
aboriginal stock. We have proofs that this is not so in some cases, in
which exact records have been kept; thus, to give a very trifling
instance, the steadily-increasing size of the common gooseberry may be
quoted. We see an astonishing improvement in many florists' flowers,
when the flowers of the present day are compared with drawings made
only twenty or thirty years ago. When a race of plants is once pretty
well established, the seed-raisers do not pick out the best plants,
but merely go over their seed-beds, and pull up the 'rogues,' as they
call the plants that deviate from the proper standard. With animals
this kind of selection is, in fact, also followed; for hardly any one
is so careless as to allow his worst animals to breed.

In regard to plants, there is another means of observing the
accumulated effects of selection namely, by comparing the
diversity of flowers in the different varieties of the same species in
the flower-garden; the diversity of leaves, pods, or tubers, or
whatever part is valued, in the kitchen-garden, in comparison with the
flowers of the same varieties; and the diversity of fruit of the same
species in the orchard, in comparison with the leaves and
flowers of the same set of varieties. See how different the leaves of
the cabbage are, and how extremely alike the flowers; how unlike the
flowers of the heartsease are, and how alike the leaves; how much the
fruit of the different kinds of gooseberries differ in size, colour,
shape, and hairiness, and yet the flowers present very slight
differences. It is not that the varieties which differ largely in some
one point do not differ at all in other points; this is hardly ever,
perhaps never, the case. The laws of correlation of growth, the
importance of which should never be overlooked, will ensure some
differences; but, as a general rule, I cannot doubt that the continued
selection of slight variations, either in the leaves, the flowers, or
the fruit, will produce races differing from each other chiefly in
these characters.

It may be objected that the principle of selection has been reduced
to methodical practice for scarcely more than three-quarters of a
century; it has certainly been more attended to of late years, and
many treatises have been published on the subject; and the result, I
may add, has been, in a corresponding degree, rapid and important. But
it is very far from true that the principle is a modern discovery. I
could give several references to the full acknowledgement of the
importance of the principle in works of high antiquity. In rude and
barbarous periods of English history choice animals were often
imported, and laws were passed to prevent their exportation: the
destruction of horses under a certain size was ordered, and this may
be compared to the 'roguing' of plants by nurserymen. The principle
of selection I find distinctly given in an ancient Chinese
encyclopaedia. Explicit rules are laid down by some of the Roman
classical writers. From passages in Genesis, it is clear that the
colour of domestic animals was at that early period attended to.
Savages now sometimes cross their dogs with wild canine animals, to
improve the breed, and they formerly did so, as is attested by
passages in Pliny. The savages in South Africa match their draught
cattle by colour, as do some of the Esquimaux their teams of dogs.
Livingstone shows how much good domestic breeds are valued by the
negroes of the interior of Africa who have not associated with
Europeans. Some of these facts do not show actual selection, but they
show that the breeding of domestic animals was carefully
attended to in ancient times, and is now attended to by the lowest
savages. It would, indeed, have been a strange fact, had attention not
been paid to breeding, for the inheritance of good and bad qualities
is so obvious.

At the present time, eminent breeders try by methodical selection,
with a distinct object in view, to make a new strain or sub-breed,
superior to anything existing in the country. But, for our purpose, a
kind of Selection, which may be called Unconscious, and which results
from every one trying to possess and breed from the best individual
animals, is more important. Thus, a man who intends keeping pointers
naturally tries to get as good dogs as he can, and afterwards breeds
from his own best dogs, but he has no wish or expectation of
permanently altering the breed. Nevertheless I cannot doubt that this
process, continued during centuries, would improve and modify any
breed, in the same way as Bakewell, Collins, &c., by this very
same process, only carried on more methodically, did greatly modify,
even during their own lifetimes, the forms and qualities of their
cattle. Slow and insensible changes of this kind could never be
recognised unless actual measurements or careful drawings of the
breeds in question had been made long ago, which might serve for
comparison. In some cases, however, unchanged or but little changed
individuals of the same breed may be found in less civilised
districts, where the breed has been less improved. There is reason to
believe that King Charles's spaniel has been unconsciously modified to
a large extent since the time of that monarch. Some highly competent
authorities are convinced that the setter is directly derived from the
spaniel, and has probably been slowly altered from it. It is known
that the English pointer has been greatly changed within the last
century, and in this case the change has, it is believed, been chiefly
effected by crosses with the fox-hound; but what concerns us is, that
the change has been effected unconsciously and gradually, and yet so
effectually, that, though the old Spanish pointer certainly came from
Spain, Mr Barrow has not seen, as I am informed by him, any native dog
in Spain like our pointer.

By a similar process of selection, and by careful training, the
whole body of English racehorses have come to surpass in
fleetness and size the parent Arab stock, so that the latter, by the
regulations for the Goodwood Races, are favoured in the weights they
carry. Lord Spencer and others have shown how the cattle of England
have increased in weight and in early maturity, compared with the
stock formerly kept in this country. By comparing the accounts given
in old pigeon treatises of carriers and tumblers with these breeds as
now existing in Britain, India, and Persia, we can, I think, clearly
trace the stages through which they have insensibly passed, and come
to differ so greatly from the rock-pigeon.

Youatt gives an excellent illustration of the effects of a course
of selection, which may be considered as unconsciously followed, in so
far that the breeders could never have expected or even have wished to
have produced the result which ensued namely, the production
of two distinct strains. The two flocks of Leicester sheep kept by Mr
Buckley and Mr Burgess, as Mr Youatt remarks, 'have been purely bred
from the original stock of Mr Bakewell for upwards of fifty years.
There is not a suspicion existing in the mind of any one at all
acquainted with the subject that the owner of either of them has
deviated in any one instance from the pure blood of Mr Bakewell's
flock, and yet the difference between the sheep possessed by these two
gentlemen is so great that they have the appearance of being quite
different varieties.'

If there exist savages so barbarous as never to think of the
inherited character of the offspring of their domestic animals, yet
any one animal particularly useful to them, for any special purpose,
would be carefully preserved during famines and other accidents, to
which savages are so liable, and such choice animals would thus
generally leave more offspring than the inferior ones; so that in this
case there would be a kind of unconscious selection going on. We see
the value set on animals even by the barbarians of Tierra del Fuego,
by their killing and devouring their old women, in times of dearth, as
of less value than their dogs.

In plants the same gradual process of improvement, through the
occasional preservation of the best individuals, whether or not
sufficiently distinct to be ranked at their first appearance as
distinct varieties, and whether or not two or more species or
races have become blended together by crossing, may plainly be
recognised in the increased size and beauty which we now see in the
varieties of the heartsease, rose, pelargonium, dahlia, and other
plants, when compared with the older varieties or with their
parent-stocks. No one would ever expect to get a first-rate heartsease
or dahlia from the seed of a wild plant. No one would expect to raise
a first-rate melting pear from the seed of a wild pear, though he
might succeed from a poor seedling growing wild, if it had come from a
garden-stock. The pear, though cultivated in classical times, appears,
from Pliny's description, to have been a fruit of very inferior
quality. I have seen great surprise expressed in horticultural works
at the wonderful skill of gardeners, in having produced such splendid
results from such poor materials; but the art, I cannot doubt, has
been simple, and, as far as the final result is concerned, has been
followed almost unconsciously. It has consisted in always cultivating
the best known variety, sowing its seeds, and, when a slightly better
variety has chanced to appear, selecting
it, and so onwards. But the gardeners of the classical period, who
cultivated the best pear they could procure, never thought what
splendid fruit we should eat; though we owe our excellent fruit, in
some small degree, to their having naturally chosen and preserved the
best varieties they could anywhere find.

A large amount of change in our cultivated plants, thus slowly and
unconsciously accumulated, explains, as I believe, the well-known
fact, that in a vast number of cases we cannot recognise, and
therefore do not know, the wild parent-stocks of the plants which have
been longest cultivated in our flower and kitchen gardens. If it has
taken centuries or thousands of years to improve or modify most of our
plants up to their present standard of usefulness to man, we can
understand how it is that neither Australia, the Cape of Good Hope,
nor any other region inhabited by quite uncivilised man, has afforded
us a single plant worth culture. It is not that these countries, so
rich in species, do not by a strange chance possess the aboriginal
stocks of any useful plants, but that the native plants have not been
improved by continued selection up to a standard of perfection
comparable with that given to the plants in countries
anciently civilised.

In regard to the domestic animals kept by uncivilised man, it
should not be overlooked that they almost always have to struggle for
their own food, at least during certain seasons. And in two countries
very differently circumstanced, individuals of the same species,
having slightly different constitutions or structure, would often
succeed better in the one country than in the other, and thus by a
process of 'natural selection,' as will hereafter be more fully
explained, two sub-breeds might be formed. This, perhaps, partly
explains what has been remarked by some authors, namely, that the
varieties kept by savages have more of the character of species than
the varieties kept in civilised countries.

On the view here given of the all-important part which selection by
man has played, it becomes at once obvious, how it is that our
domestic races show adaptation in their structure or in their habits
to man's wants or fancies. We can, I think, further understand the
frequently abnormal character of our domestic races, and likewise
their differences being so great in external characters and relatively
so slight in internal parts or organs. Man can hardly select, or only
with much difficulty, any deviation of structure excepting such as is
externally visible; and indeed he rarely cares for what is internal.
He can never act by selection, excepting on variations which are first
given to him in some slight degree by nature. No man would ever try to
make a fantail, till he saw a pigeon with a tail developed in some
slight degree in an unusual manner, or a pouter till he saw a pigeon
with a crop of somewhat unusual size; and the more abnormal or unusual
any character was when it first appeared, the more likely it would be
to catch his attention. But to use such an expression as trying to
make a fantail, is, I have no doubt, in most cases, utterly incorrect.
The man who first selected a pigeon with a slightly larger tail,
never dreamed what the descendants of that pigeon would become through
long-continued, partly unconscious and partly methodical selection.
Perhaps the parent bird of all fantails had only fourteen
tail-feathers somewhat expanded, like the present Java fantail, or
like individuals of other and distinct breeds, in which as
many as seventeen tail-feathers have been counted. Perhaps the first
pouter-pigeon did not inflate its crop much more than the turbit now
does the upper part of its oesophagus, a habit which is
disregarded by all fanciers, as it is not one of the points of the
breed.

Nor let it be thought that some great deviation of structure would
be necessary to catch the fancier's eye: he perceives extremely small
differences, and it is in human nature to value any novelty, however
slight, in one's own possession. Nor must the value which would
formerly be set on any slight differences in the individuals of the
same species, be judged of by the value which would now be set on
them, after several breeds have once fairly been established. Many
slight differences might, and indeed do now, arise amongst pigeons,
which are rejected as faults or deviations from the standard of
perfection of each breed. The common goose has not given rise to any
marked varieties; hence the Thoulouse and the common breed, which
differ only in colour, that most fleeting of characters, have lately
been exhibited as distinct at our poultry-shows.

I think these views further explain what has sometimes been noticed
namely that we know nothing about the origin or history of any
of our domestic breeds. But, in fact, a breed, like a dialect of a
language, can hardly be said to have had a definite origin. A man
preserves and breeds from an individual with some slight deviation of
structure, or takes more care than usual in matching his best animals
and thus improves them, and the improved individuals slowly spread in
the immediate neighbourhood. But as yet they will hardly have a
distinct name, and from being only slightly valued, their history will
be disregarded. When further improved by the same slow and gradual
process, they will spread more widely, and will get recognised as
something distinct and valuable, and will then probably first receive
a provincial name. In semi-civilised countries, with little free
communication, the spreading and knowledge of any new sub-breed will
be a slow process. As soon as the points of value of the new sub-breed
are once fully acknowledged, the principle, as I have called it, of
unconscious selection will always tend, perhaps more at one
period than at another, as the breed rises or falls in
fashion, perhaps more in one district than in another,
according to the state of civilisation of the inhabitants
slowly to add to the characteristic features of the breed, whatever
they may be. But the chance will be infinitely small of any record
having been preserved of such slow, varying, and insensible changes.

I must now say a few words on the circumstances, favourable, or the
reverse, to man's power of selection. A high degree of variability is
obviously favourable, as freely giving the materials for selection to
work on; not that mere individual differences are not amply
sufficient, with extreme care, to allow of the accumulation of a large
amount of modification in almost any desired direction. But as
variations manifestly useful or pleasing to man appear only
occasionally, the chance of their appearance will be much increased by
a large number of individuals being kept; and hence this comes to be
of the highest importance to success. On this principle Marshall has
remarked, with respect to the sheep of parts of Yorkshire, that 'as
they generally belong to poor people, and are mostly
in small lots, they never can be improved.' On
the other hand, nurserymen, from raising large stocks of the same
plants, are generally far more successful than amateurs in getting new
and valuable varieties. The keeping of a large number of individuals
of a species in any country requires that the species should be placed
under favourable conditions of life, so as to breed freely in that
country. When the individuals of any species are scanty, all the
individuals, whatever their quality may be, will generally be allowed
to breed, and this will effectually prevent selection. But probably
the most important point of all, is, that the animal or plant should
be so highly useful to man, or so much valued by him, that the closest
attention should be paid to even the slightest deviation in the
qualities or structure of each individual. Unless such attention be
paid nothing can be effected. I have seen it gravely remarked, that it
was most fortunate that the strawberry began to vary just when
gardeners began to attend closely to this plant. No doubt the
strawberry had always varied since it was cultivated, but the slight
varieties had been neglected. As soon, however, as gardeners picked
out individual plants with slightly larger, earlier, or
better fruit, and raised seedlings from them, and again picked out the
best seedlings and bred from them, then, there appeared (aided by some
crossing with distinct species) those many admirable varieties of the
strawberry which have been raised during the last thirty or forty
years.

In the case of animals with separate sexes, facility in preventing
crosses is an important element of success in the formation of new
races, at least, in a country which is already stocked with
other races. In this respect enclosure of the land plays a part.
Wandering savages or the inhabitants of open plains rarely possess
more than one breed of the same species. Pigeons can be mated for
life, and this is a great convenience to the fancier, for thus many
races may be kept true, though mingled in the same aviary; and this
circumstance must have largely favoured the improvement and formation
of new breeds. Pigeons, I may add, can be propagated in great numbers
and at a very quick rate, and inferior birds may be freely rejected,
as when killed they serve for food. On the other hand, cats, from
their nocturnal rambling habits, cannot be matched, and, although so
much valued by women and children, we hardly ever see a distinct breed
kept up; such breeds as we do sometimes see are almost always imported
from some other country, often from islands. Although I do not doubt
that some domestic animals vary less than others, yet the rarity or
absence of distinct breeds of the cat, the donkey, peacock, goose,
&c., may be attributed in main part to selection not having been
brought into play: in cats, from the difficulty in pairing them; in
donkeys, from only a few being kept by poor people, and little
attention paid to their breeding; in peacocks, from not being very
easily reared and a large stock not kept; in geese, from being
valuable only for two purposes, food and feathers, and more especially
from no pleasure having been felt in the display of distinct breeds.

To sum up on the origin of our Domestic Races of animals and
plants. I believe that the conditions of life, from their action on
the reproductive system, are so far of the highest importance as
causing variability. I do not believe that variability is an
inherent and necessary contingency, under all circumstances,
with all organic beings, as some authors have thought. The effects of
variability are modified by various degrees of inheritance and of
reversion. Variability is governed by many unknown laws, more
especially by that of correlation of growth. Something may be
attributed to the direct action of the conditions of life. Something
must be attributed to use and disuse. The final result is thus
rendered infinitely complex. In some cases, I do not doubt that the
intercrossing of species, aboriginally distinct, has played an
important part in the origin of our domestic productions. When in any
country several domestic breeds have once been established, their
occasional intercrossing, with the aid of selection, has, no doubt,
largely aided in the formation of new sub-breeds; but the importance
of the crossing of varieties has, I believe, been greatly exaggerated,
both in regard to animals and to those plants which are propagated by
seed. In plants which are temporarily propagated by cuttings, buds,
&c., the importance of the crossing both of distinct species and
of varieties is immense; for the cultivator here quite disregards the
extreme variability both of hybrids and mongrels, and the frequent
sterility of hybrids; but the cases of plants not propagated by seed
are of little importance to us, for their endurance is only temporary.
Over all these causes of Change I am convinced that the accumulative
action of Selection, whether applied methodically and more quickly, or
unconsciously and more slowly, but more efficiently, is by far the
predominant power.